Conventional piston damper assemblies include a piston damper and a relative velocity sensor. The piston damper includes an annularly-cylindrical damper body, includes a ferromagnetic piston rod which is axially movable within the damper body and which extends axially outward from a first end of the damper body and is attached to the vehicle frame, and includes a ferromagnetic dust tube which circumferentially surrounds the damper body and which is attached to the piston rod. The relative velocity sensor has a magnet and a coil. The magnet is an annular disc magnet which circumferentially surrounds the piston rod and which is attached to the first end of the damper body. The coil is an axially-distributed coil which is coaxially aligned with the piston rod, which axially extends the entire length of the piston rod travel, and which is attached to the inside of the dust tube. The piston rod acts as a magnetic flux carrier with the flux exiting the damper body in the radial direction across a cylindrical gap to the axially-distributed coil on the dust tube. The voltage induced in the coil due to the motion of the damper body relative to the dust tube is proportional to the relative velocity of the damper body relative to the dust tube. The operation of a conventional a relative velocity sensor is well understood in the art. However, with dampers having relatively long strokes (such as a stroke greater than four times the inside diameter of the damper body), a conventional relative velocity sensor provides inaccurate relative velocity measurements because of the flux leakage from the piston rod. Also, when the piston damper is an MR (magnetorheological) damper, the flux produced by the MR solenoid interferes with a conventional relative velocity sensor causing inaccurate relative velocity measurements.
What is needed is an improved piston damper assembly, and an improved dust tube subassembly thereof, having a velocity sensor.